You don't bring chairs on a backpacking trip. You bring your sleeping pad/mat. If it is a foam mat it can be used almost anywhere.
Try to pack minimally. It isn't fun to deal with someone who is complaining about their pack weight or someone who has other people carry their gear.
If it is only a weekend backpacking trip he should only bring one change of underwear, two extra pairs of socks, the shirt he's wearing, the pants he's wearing, a hat, boots, a light jacket unless it's a cold area (bring a small fleece jacket, he'll stay warm), some food, especially trail snacks (powerbars, trail mix), a flashlight, sleeping bag, sleeping pad, a knife, and maybe a small pair of gloves.
